A conventionally known lens barrel includes a fixed cylinder having a guide groove extending along an optical axis direction, a cam cylinder rotatably disposed with respect to the fixed cylinder and having a cam groove, a cam follower configured to slide on the cam groove and move along the guide groove of the fixed cylinder, and a lens holding member supporting the cam follower and configured to move in the optical axis direction together with the cam follower.
As such a lens barrel having the above-described configuration, Patent Document 1, for example, discloses a lens barrel in which a cam follower is biased radially outward by a cam follower biasing member so that a cam groove contact portion constituted by a frustoconical circumferential surface at a radially outside tip of the cam follower is pressed against an inner surface of the cam groove.
Patent Document 2, for example, discloses an image taking device including a lens barrel having three impact-resistance cam grooves in addition to three driving cam grooves. The impact-resistance cam grooves form a predetermined clearance with respect to cam followers in a normal operation so as to prevent deformation of the driving cam grooves or the cam followers or displacement of the cam followers from the cam grooves when an impact is applied to the lens barrel.
However, since the cam groove contact portion of the cam follower is constituted by the frustoconical circumferential surface in Patent Document 1, the cam groove contact portion of the cam follower is in line contact with the cam groove, and thus, the contact area between the cam groove contact portion and the cam groove is small. Accordingly, when an impact is applied to the lens barrel, the cam follower is displaced from the cam groove, resulting in deformation of the cam follower and/or the cam groove.
On the other hand, in the lens barrel disclosed in Patent Document 2, even when an impact is applied to the lens barrel, the cam followers are less likely to be displaced from the cam grooves and the cam followers and/or the cam grooves are less likely to be deformed because of the three impact-resistance cam grooves and the cam followers fitted in the cam grooves. In the lens barrel disclosed in Patent Document 2, however, the three impact-resistance cam grooves are formed in addition to the three driving cam grooves. Accordingly, a larger space is necessary to form cam grooves comparing to the configuration of only the driving cam grooves, leading to an increase in the size of the unit. In addition, the impact-resistance cam grooves and the impact-resistance cam followers need to be accurately formed in order to prevent deformation of the can grooves and the cam followers. This requires considerable time and cost for fabrication.